1. Field of the Invention
The present invention relates generally to gas turbine engine, and more specifically to a stator vane with endwall cooling.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine, such as an industrial gas turbine (IGT) engine, a turbine includes one or more rows of stator vanes and rotor blades that react with a hot gas stream from a combustor to produce mechanical work. The stator vanes guide the gas stream into the adjacent and downstream row of rotor blades. The first stage vanes and blades are exposed to the highest gas stream temperatures and therefore require the most amount of cooling.
One major problem with the first stage stator vanes is erosion from hot spots that occur on certain locations around the vane leading edge fillet regions due to migration of the has gas stream. This erosion results in cracking of the metal or spallation of the TBC to expose the metal surface to the hot gas stream. FIG. 1 shows a hot gas stream flow pattern in a row of stator vanes. The hot flow core gas entering the turbine stator vanes is formed of a boundary layer 11 and a stream surface 12. The boundary layer 12 entering the row of vanes collides with the leading edge of the vane airfoil and forms a horseshoe vortex that separates into pressure side vortices 13 and suction side vortices 14. The pressure side (P/S) vortices 13 will flow downward and flow along the airfoil pressure side forward fillet region first. Due to the presence of hot flow channel pressure gradient from the pressure side to the suction side, the pressure side vortices 13 will migrate across the hot gas passage and end up flowing along the suction side of the adjacent vane. As the pressure side vortices 13 rolls across the hot flow channel, the size and strength of the pressure side vortices 13 becomes larger and stronger. Since the pressure side vortices 13 is much stronger than the suction side (S/S) vortices 14, the suction side vortices 14 will flow along the airfoil suction side fillet and function as a counter flow vortices for the pressure side vortices 13. The P/S vortices 13 and the S/S vortices 14 are counter rotating vortices.
FIG. 1 shows an isometric view of the stator vanes with the vortices formation for a boundary layer entering the turbine airfoil. As a result of these vortices flow phenomena, some of the hot core gas flow from the upper airfoil span flows toward a close proximity to the endwall and therefore creates a high heat transfer coefficient and a high gas temperature region at the airfoil fillet region.
As shown in FIG. 1, the resulting forces drive the stagnated flow that occurs along the airfoil leading edge towards the region of lower pressure at the intersection of the airfoil and endwall. This secondary flow flows around the airfoil leading edge fillet and endwall region. This secondary flow then rolls away from the airfoil leading edge and flows upstream along the endwall against the hot core gas flow. As a result, the stagnated flow forces acting on the hot core gas and radial transfer of hot core gas flow from the upper airfoil span toward close proximity to the endwall creates a high heat transfer coefficient and a high gas temperature region at the intersection location. For the endwall with film cooling and vortex flow within the flow channel, the vortex flow within the flow channel will degrade the film cooling effectiveness level.
Another effect on the vanes from the hot gas stream reacting with the leading edge of the vanes is shown in FIGS. 2 and 3. Besides the P/S and S/S vortices forming, a forward stagnated flow 15 forms along the leading edge adjacent to the inner endwall 22 and outer endwall 21 in which the hot gas flow flows back toward the oncoming hot gas stream. A secondary flow 16 along the fillet region on both the P/S and the S/S of the airfoil is also formed as represented by the arrows in FIG. 3. A downdraft secondary flow also appears on the stagnation point of the airfoil leading edge surface. An area of stagnation flow occurs in this region creates a high heat transfer coefficient and high gas temperature region.